1. Field of the Invention
The present invention relates to a film thickness measuring device and to a measuring method for measuring a thickness of a film on a wafer, and further to a wafer polishing apparatus for polishing a film while measuring the thickness of a film on a wafer in-process.
2. Description of the Related Art
Recently, in manufacturing processes of semiconductor devices, a technique has been commonly used where aluminum or the like is evaporated onto a mirror finished surface of a wafer to form circuit patterns. An insulating film such as SiO.sub.2 is formed thereon. Thereafter, the insulating film is flattened by polishing and further construction of the devices are sequentially structured thereon.
In polishing the film formed on the wafer as described above, it is very important to measure the thickness of the film precisely. As means for measuring the thickness, a light interference film thickness meter has been employed. The light interference film thickness meter, as is generally known, measures the thickness of the film by irradiating a light emitted from a light irradiation portion on the surface of the wafer, receiving the reflected light at the light irradiation portion and detecting interference of the reflected light at the top surface of the film and the reflected light at the bottom surface of the film. This film thickness meter, however, has a drawback because the thickness of the film cannot be measured unless the surface to be measured is cleaned.
Accordingly, it has been difficult to perform thickness measurement using the light interference film thickness meter during a wafer polishing step to control the amount of polishing. In addition, when using other indirect measuring methods where the film thickness can be measured regardless of the cleanliness of the wafer, a high accuracy required for the film polishing cannot be obtained.
The present invention has been made in consideration of the circumstances as described above, and has its object to provide a film thickness measuring apparatus, a film thickness measuring method and a wafer polishing system which can measure the thickness of the film with high accuracy during a polishing step of the wafer.